The effect of methionine sulphoximine on the absorption of ammonium by maize and barley roots over short periods
1993
Lee, R.B. | Ayling, S.M.
Pre-treating intact, ammonium-grown plants of maize and barley with the glutamine synthetase inhibitor, L-methionine sulphoximine (MSO), increased subsequent accumulation of 13N or 15N from labelled ammonium very markedly--up to 8-fold in extreme cases. The phenomenon could not be satisfactorily explained in terms of an effect of MSO on the cation-exchange properties of the root free space, because neither potassium (86Rb+) nor sodium absorption was enhanced by MSO pretreatment, and rapid absorption of ammonium continued for too long in relation to the likely free-space content of a monovalent cation. Instead, the response is seen as a consequence of the enlargement of the cytoplasmic and vacuolar ammonium pools that occurs when ammonium assimilation is inhibited by MSO. The results, which included comparisons between short-term and longer-term rates of ammonium absorption, provide tentative evidence of rapid fluxes of ammonium through the plasma membrane.
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